A varistor is an active component of a device for protecting an electrical installation, such as a lightning arrester. Current varistors, or variable resistors comprise a ceramic block for example composed of zinc oxide assembled by sintering and have a non-linear current/voltage characteristic: beyond a certain voltage threshold, the varistor impedance drops to allow the discharge of current following a voltage surge. When the voltage returns to its normal level, the varistor impedance assumes its value at the standby state.
In a lightning arrester, one or several varistors are generally disposed in a cartridge also comprising a connection element, allowing to electrically connect them to the electrical installation to be protected.
In order to prevent damage due to malfunctions and to abnormal heating phenomena of the varistors, the latter must be fitted with a disconnection system. This leads for a need to equip lightening arresters with systems for indicating a connected or disconnected state of the varistors.
It is known to use indication systems comprising electrical lights mounted in parallel on the varistors. The use of electrical lights leads to permanent energy consumption.
It is also known to use mechanical indication systems requiring the use of several expensive and bulky pieces which lead to a blocking risk of the mechanism.